1. Field of the Invention
The present invention relates to a steam sensitive composition and a sterilization indicator composition which markedly change in color upon exposure to steam sterilization treatment. More particularly, the present invention relates to a steam sensitive composition and a sterilization indicator composition which may be incorporated in steam sensitive paints or inks used in the packaging of medical instruments, retort foods, etc., and other steam sterilizable articles. These steam sensitive paints or inks change color upon exposure to a steam sterilization process of a prescribed temperature for a prescribed period of time.
2. Background
Steam sensitive compositions and sterilization indicator compositions which contain as main components a metal compound, such as lead carbonate, and sulfur, have so far generally been used. U.S. Pat. No. 2,889,799 disclosed such compositions. Such sterilization marking inks are disclosed in JP-B-45-4690. Further, heat sensitive compositions utilizing a color change at the time of formation or decomposition of metal complexes are disclosed in JP-A-51-3381. Further, examples of the application of steam sensitive compositions to inks are disclosed in JP-B-55-18464 and JP-B-59-13550.
However, the conventional steam sensitive compositions and sterilization indicator compositions are not always satisfactory for one or more of the following reasons:
1) Color development is limited to black or other dark colors. PA1 2) Since color change begins as soon as a definite temperature is reached, it is impossible to confirm whether or not treatment with steam and for the period of time essential to accomplish sterilization has been completed. PA1 3) The components of the compositions are sublimable, so that the storage stability is poor and color change may not occur uniformly. PA1 4) There is an offensive odor, particularly with compositions containing sulfur. PA1 1) The composition exhibits a remarkable color change only when all of the conditions for steam sterilization, i.e. time, temperature and steam have been satisfied. PA1 2) The has good storage stability. Specifically, the steam sensitive compositions do not react at low temperature (e.g. room temperature); are insoluble in and nonreactive with water; and are not sublimable. PA1 3) The composition exhibits a color change after steam sterilization which is uniform and distinguishable. PA1 4) The composition is odorless.
Particularly, those which utilize the formation reaction of metal complexes easily change in color with heat alone, so that it is difficult to confirm whether or not steam is present for the necessary period of time. Both those which utilize the formation reaction of metal complexes and those which utilize the decomposition reaction of metal complexes are lacking in storage stability. Particularly those which utilize the decomposition reaction of metal complexes exhibit instability, to moisture such as humidity in air, etc.